Estimation of Residual Nickel and Some Heavy Metals in Vanaspati Ghee Hizbullah Khan, a Mohammad Fida, b Imdad Ullah Mohammadzai c * and Mumtaz Khan d a Department of Environmental Sciences, University of Peshawar, Pakistan b NCE in Physical Chemistry, University of Peshawar, Pakistan c Institute of Chemical Sciences, University of Peshawar, 25120, Peshawar, Pakistan d PCSIR Laboratories Complex Peshawar, Pakistan To convert vegetable edible oils into vanaspati ghee, nickel is used as a catalyst in the hydrogenation process. A simple and fast method for the trace level determination of nickel in ghee is reported. In this work different methods were applied for the extraction of residual nickel from ghee samples. Using tolu- ene, benzene and carbon tetrachloride as organic solvents, an acid mixture was used for the extraction of nickel. Extracted nickel was quantified with atomic absorption and colorimetric methods. Among the or- ganic solvents, toluene proved to be the best solvent mediating a 95% extraction of nickel from ghee sam- ples. Nickel was extracted and determined in ten different brands of ghee and in all samples its amount was well above the permissible limit of WHO (0.2 mg/g). Other metals like lead, zinc, copper, and cadmium were also determined and their concentrations were found to be much below the WHO permissible limits. Keywords: Hydrogenated edible oil; Nickel formate catalyst; Solvent extraction; Spectrophoto- metric quantification. INTRODUCTION The human body uses oils and fats in the diet for three purposes, as an energy source, as a structural component and to make powerful biological regulators. Oils and fats also play an important role in metabolic reactions in the hu- man body. Oils and fats contain fatty acids, which are sus- ceptible to attack by a number of agents e.g. light, oxygen, metals, etc. 1 Bad flavor known as rancidity is produced by the oxidation of fats. Catalytic hydrogenation and/or use of antioxidants can suppress or eliminate rancidity. Fats and oils consist of three fatty acids chemically combined with a molecule of glycerol to form triglyceride. All vegetable ed- ible oils mostly have polyunsaturated and monounsatu- rated fatty acids, while fats consist mostly of saturated fatty acids. Catalytic hydrogenation of vegetable oils into ghee increases the level of saturation in the hydrocarbon chain and a corresponding increase in the melting point of the product is generally observed. Nickel, supported on an in- ert carrier, is widely used as catalyst in this process and is removed from the ghee after the hydrogenation process is completed. Hydrogenated oils are generally contaminated with catalyst due to faulty filtration or intentional non- removal of catalyst to lower the cost of production. This paper deals with a more rapid, economical and efficient method for the extraction of nickel from ghee. Several methods are available for the extraction of nickel from the hydrogenated product. 2,3 These extraction pro- cesses have not yet produced the desired results, are cum- bersome, time consuming and non-efficient for maximum extraction. This often leads to the wrong conclusion about the quality of ghee. In this work, several organic solvents were tested for dissolution, and improvements in the existing methods were checked and applied. Besides nickel, other metals were also determined using AAS and spectrophotometric methods. Environmental Levels and Human Exposure Nickel levels in terrestrial and aquatic organisms can vary over several orders of magnitude. Typical atmospheric nickel levels for human exposure range from about 5 to 35 ng/m 3 at rural and urban sites, leading to a nickel uptake via inhalation of 0.1-0.7 mg/day. Nickel in the drinking-water is generally less than 10 mg/L, but occasionally may be re- leased from the plumbing fittings, resulting in concentra- tions of up to 500 mg/litre. 4 Nickel concentrations in food are usually below 0.5 mg/kg fresh weight. Daily intake of nickel from food will vary widely because of different dietary habits and can Journal of the Chinese Chemical Society, 2007, 54, 737-741 737